1. Technical Field
The present invention relates to a method of manufacturing a printed circuit board having metal bumps.
2. Description of the Related Art
With the recent advancement of the electronics industry, electronic components are being developed to have high performance and thus there is a demand for miniaturized and highly-densified packages. Accordingly, interposers (substrates) which function to connect ICs to a main board must be more densely packed. The high densification of packages is attributable to an increase of the number of I/Os of the ICs, and the method of connection made with the interposers has also been made more efficient. As methods of mounting ICs on a board to manufacture a high density package, a wire bonding process or a flip bonding process are currently being used. In this regard, as the number of I/Os is increased above a certain number, the flip bonding process is preferably used because of the increase in the manufacturing costs.
In order to perform the flip chip bonding process, the formation of solder balls is required. According to a conventional method, the solder balls are formed through a printing process of solder paste using screen printing and a reflow process.
However, the method of forming bumps of a printed circuit board using a printing technique is problematic in that it requires wide connecting pads, so that it is difficult to realize bumps having fine pitch of 120 μm or less.
Further, the method of forming the bumps using the printing technique is problematic in that it is difficult to form bumps at fine pitch, or their volume is excessively decreased even if the bumps are formed.
Since the connecting pads are formed using a plating technique, the connecting pads may vary in thickness because of errors in plating, and it is hard to evenly distribute the amount of solder paste used when printing it during the printing process, so that the height of the solder balls is not uniform, and thus solder balls which are not connected to a semiconductor chip may be found.
Furthermore, since the height difference between a solder resist and the pads is large, voids may undesirably occur during an underfill process subsequent to the mounting of electronic components.